This invention relates generally to conduits for transporting fluids, and more specifically to unitary conduits for transporting fuel into fuel nozzles used in gas turbine engines.
Turbine engines typically include a plurality of fuel nozzles for supplying fuel to the combustor in the engine. The fuel is introduced at the front end of a burner in a highly atomized spray from a fuel nozzle. Compressed air flows around the fuel nozzle and mixes with the fuel to form a fuel-air mixture, which is ignited by the burner. Because of limited fuel pressure availability and a wide range of required fuel flow, many fuel injectors include pilot and main nozzles, with only the pilot nozzles being used during start-up, and both nozzles being used during higher power operation. The flow to the main nozzles is reduced or stopped during start-up and lower power operation. Such injectors can be more efficient and cleaner-burning than single nozzle fuel injectors, as the fuel flow can be more accurately controlled and the fuel spray more accurately directed for the particular combustor requirement. The pilot and main nozzles can be contained within the same nozzle assembly or can be supported in separate nozzle assemblies. These dual nozzle fuel injectors can also be constructed to allow further control of the fuel for dual combustors, providing even greater fuel efficiency and reduction of harmful emissions. The temperature of the ignited fuel-air mixture can reach an excess of 3500° F. (1920° C.). It is therefore important that the fuel supply conduits, flow passages and distribution systems are substantially leak free and are protected from the flames and heat.
Over time, continued exposure to high temperatures during turbine engine operations may induce thermal stresses in the conduits and fuel nozzles which may damage the conduits or fuel nozzle and may adversely affect their operation. For example, thermal stresses may cause fuel flow reductions in the conduits and may lead to excessive fuel maldistribution within the turbine engine. Furthermore, over time, continued operation with damaged fuel nozzles may result in decreased turbine efficiency, turbine component distress, and/or reduced engine exhaust gas temperature margin.
Improving the life cycle of fuel nozzles installed within the turbine engine may extend the longevity of the turbine engine. Known fuel nozzles include a delivery system and a support system. The delivery system comprising conduits for transporting fluids delivers fuel to the turbine engine and is supported, and is shielded within the turbine engine, by the support system. More specifically, known support systems surround the delivery system, and as such are subjected to higher temperatures and have higher operating temperatures than delivery systems which are cooled by fluid flowing through the fuel nozzle. It may be possible to reduce the thermal stresses in the conduits and fuel nozzles by configuring their external and internal contours and thicknesses.
Conventional gas turbine engine components such as, for example, fuel nozzles and their associated conduits, are generally expensive to fabricate and/or repair because the conventional fuel nozzle designs having complex conduits for transporting fuel include a complex assembly and joining of more than thirty components. More specifically, the use of braze joints can increase the time needed to fabricate such components and can also complicate the fabrication process for any of several reasons, including: the need for an adequate region to allow for braze alloy placement; the need for minimizing unwanted braze alloy flow; the need for an acceptable inspection technique to verify braze quality; and, the necessity of having several braze alloys available in order to prevent the re-melting of previous braze joints. Moreover, numerous braze joints may result in several braze runs, which may weaken the parent material of the component. The presence of numerous braze joints can undesirably increase the weight and manufacturing cost of the component.
Accordingly, it would be desirable to have conduits for transporting fluids such as, for example, fuel supply conduits for fuel nozzles, that have unitary construction for reducing potential leakage and other undesirable effects described earlier. It is desirable to have fluid supply conduits with complex geometries having a unitary construction to reduce the cost and for ease of assembly. It is desirable to have a method of manufacturing unitary conduits having complex three-dimensional geometries for transporting fluids, such as fuel supply conduits for fuel nozzles.